1. Technical Field
The present disclosure relates to magnetorheological fluid damping, and, in particular, to a system and method for magnetorheological-fluid damping utilizing porous media.
2. Description of Related Art
Generally, magnetorheological fluids (herein referred to as “MR” fluids) are a class of fluids that change in viscosity in the presence of a magnetic field. An MR fluid may have the viscosity of commercially available motor oil when no magnetic field is present and may behave similarly to a solid when a magnetic field is applied (e.g., it may become a viscoelastic solid). Therefore, they exhibit controllable yield strength. When no magnetic field is present, MR fluids may be sufficiently modeled as Newtonian liquids. These unique properties make the material ideal for mechanical vibration damping because of the ability to utilize a magnetic field to control the viscosity of the MR fluid. Additionally, some MR fluids have a response time of less than 10 milliseconds making it well suited for mechanical vibration damping systems.
MR fluid dampers are emerging as a promising technology for semi-active damping control. They have been widely applied to control and suppress unwanted mechanical vibrations and shock of various systems and structures because of their inherent advantages. Such advantages include its ability to assist in continuously controlling force, its fast response time, and its relatively small power consumption. Some mechanical vibration and shock mitigation systems that utilize MR fluid dampers include either a power supply and/or a current amplifier.
Many MR fluid damping systems include a hydraulic cylinder containing MR fluid, and a piston head adapted for movement within the housing. The piston head and/or hydraulic cylinder may be formed from one or more materials including ferrous metal. Additionally, the piston head may be designed to contain and/or connect to several windings of conductive wire forming a magnetic coil. For example, a magnetic coil may be embedded inside the piston head or wrapped around the piston head. Magnetic coils may be in the shape of a solenoid (sometimes referred to as “a solenoid” or “a coil”). The magnetic coil may generate a magnetic field in and around the piston to affect the MR fluid. Descriptions of various MR dampers can be found in U.S. Pat. No. 5,277,281 to J. D. Carlson et al., U.S. Pat. No. 6,279,700 to I. Lisenker et al., U.S. Pat. No. 6,311,810 to P. N. Hopkins et al., U.S. Pat. No. 6,694,856 to P. C. Chen and N. M. Wereley, and U.S. Pat. No. 6,953,108 to E. N. Anderfaas and D. Banks. In these MR damper configurations, the MR fluid pathways move with the piston (U.S. Pat. Nos. 5,277,281, 6,279,700, 6,311,810, and 6,953,108) or are fixed relative to the damper body (U.S. Pat. No. 6,694,856). The MR fluid pathways are straight or in rectilinear simple geometry shapes and are configured to be perpendicular to the magnetic field.
There has been a modern trend towards miniaturization of MR fluid valves. This trend has imposed some design constraints on the overall design of MR fluid damping systems. One MR fluid valve configuration uses tortuous channels that naturally exist in porous media, e.g., as described in the reference Shulman Z., Magnetorheological systems and their application, Magnetic Fluids and Applications Handbook (1996) pp. 188-229. This reference proposes spiral channels or packed beds of particles as flow channels placed inside a solenoid. Kuzhir et al. developed a hydraulic device for the investigation of MR fluid flow through porous media in the presence of a magnetic field parallel to the flow. (see Kuzhir P., Bossis G., Bashtovoi V. and Volkova O., Flow of magnetorheological fluid through porous media, Euro. J. Mech. B/Fluids 22 (2003) pp. 331-343) Their measurements demonstrated that a packed bed of magnetic grains had a higher controllable damping range than spiral channels. There is a continuing need for efficient and effective MR fluid damping systems utilizing MR fluid valves to control the flow of MR fluid.